Comparisons of the vertical distributions of aerosols in the CALIPSO and GEOS-Chem datasets in China

In this study, we compared the aerosol profiles derived from the Cloud-Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) over China with those simulated by the Global 3-D Atmospheric Chemical Transport model (GEOS-Chem) for the period of 2007–2014. Multiple steps were implemented in the data analysis. First, we validated CALIPSO and GEOS-Chem aerosol optical depth (AOD) using Moderate Resolution Imaging Spectroradiometer (MODIS) products, both CALIPSO and GEOS-Chem AOD were found to 30%∼50% underestimations in eastern China and 60%∼80% underestimations in western China. Second, MODIS AOD was introduced to normalize the aerosol extinction coefficient (AEC) of both CALIPSO and GEOS-Chem in each 1-km layer below 10 km to achieve a uniform comparison. Linear regression analysis between the normalized CALIPSO and GEOS-Chem AECs yielded better correlation coefficients and lower mean relative differences than the direct comparisons from the original data. Finally, we investigated the vertical distributions of aerosol components over the North, South, Northwest and Tibet regions of China. Our findings are summarized based on different aerosol components as the following. Dust aerosols: The percentages of CALIPSO polluted dust to total dust in the North and South regions (50%∼68% in different seasons) are higher than those in the Northwest and Tibet regions (25%∼45%). Thus, the polluted dust classification significantly affects our comparisons in the North and South. For CALIPSO pure dust, its concentrations in the higher layers are larger than those of GEOS-Chem. Continental/sulfate, nitrate, and ammonium (SNA) aerosols: The percentages of CALIPSO continental aerosols to total aerosols are almost negligible throughout the four regions (<10%). Even including the polluted dust in the continental aerosol, their combined contributions remain ∼10% lower than GEOS-Chem SNA. Thus, we found that the current CALIPSO aerosol classification scheme is limited in the detection of anthropogenic aerosols in China. Soot aerosols: The GEOS-Chem soot aerosol values are a factor of 2–4 times lower than those of CALIPSO. The omission of small agricultural field burnings in the GEOS-Chem emission inventory might have resulted in the soot aerosol underestimations.